Frequency modulation



G. l.. ussELMAN FREQLIENCY MODULATION Filed June 5, 1940 Oct. 13, 1942. l

:s Sheets-Sheet 1 SIG/W SUI/ECE .fx V/ E 65 SOI/BCE Oct. 13, 1942. G. l.. ussELMAN 2,298,437

' FREQUENCY MODULATION Filed June 5, 1940 s sheets-sheet 2 Figa.

50u/ace nventor Geargl. /selm Oct. 13, 1942.

G. l., ussELMAN FREQUENCY MODULATION 3 Sheets-Sheet 3 Filed June 5. 1940 :Nc LM L JIK fao N FEL/IY 0 C/Ecl//rs l TONE TELEGEF/i FILS.

CMPENSHTO TUBE Gemyell nventor t Zfrse'lnzanI 71,4%

Gttpmeg Patented Oct. 13, 1942 FREQUENCY MODULA'I'IONl George L. Usselman, Port jefferson, N. Y., assign-L or to Radio Corporation of America, a corpora- V tion of Delaware Application June5, 1940, Serial No. 338,838

j 26 Claims.

This application concerns a new and improved method of and means for producing wave energy the frequency of which is modulated in accordance with signals.

In most crystal controlled frequency modulators known heretofore, it is possible for the modulator to drive the oscillator beyond the 'crystal controlled oscillating frequency. This produces distortion in the frequency modulation process. The present invention eliminates this possibility. No frequency modulation is possible when the crystal does not oscillate. Thus, We are assured of crystal controlled oscillations during the entire modulation process in this frequency modulator. The crystal oscillator circuit used in this frequency modulator is of the aperiodic type, except for the piezo-electric crystal, having the anode grids grounded for radio frequency. These features contribute considerably to the improved operation of this circuit.' I

In describing my invention reference will be made to the attached drawings wherein;

Figs. 1 to 4, inclusive, each show the essential features of a systen for generating wave energy and modulating the frequency thereof in accordance with control potentials; and

Fig. illustrates details of a phase shifting circuit used under certain circumstances in certain of the prior modifications.

The oscillators in the circuits of Figs. 1 to 4, inclusive, are all of the same general type. IT'hese oscillators are of the crystal controlled grounded anode type in which the second grid G2 of tube vl is bypassed tc ground for radio frequency by means of condenser 4. 'I'he third grid G3 may be grounded directly as shown in Fig. l or it may be biased through a resistance 3 and bypassed to ground for radio frequency by means of a separate condenser C6 as shown in Figs. 2, 3 and 4. Both the secondand third grids in Figs. 2, 3 and 4,are lsupplied with positive potentials through resistors 3 and 3 from a source not shown by means of lead 8. Resistors 3 and 2 act as aperiodic smoothing impedances to keep radio frequency out of lead 8. The anode I0 of tube VI is supplied with positive current and potential through tank circuit CI, LI from a power source not shown. This source may be the sameas the source which supplies voltage to lead I or it may be a separate source. 'Iheoutput circuit I2 for the frequency modulator is coupled to the tank.

coil Ll as shown. In Fig. 1 this coupling is inductive. In Figs. 2, 3 and 4 this coupling is capacitive. The control grid GI of the'oscillator a point I4 between the crystal X and the neutralizing condenser N as shown in Figs. 1, 2, 3 and 4. l The potentiometer grid leak resistor RI is con- The cathode 20 of tube V2 is grounded. The control grid 24 of tube V2 is excited by high frequency oscillations becauseit is connected to a tap on resistor RI through a blocking condenser 26 as shown. Fig. 1 shows a phase shifting reactance P connected in this modulator grid radiofrequency excitation circuit.

The phase shifting network shown in. Fig. 5 may be used in place of P in Fig. 1. To include the network (Fig. 5) in the circuit in place o f P the leads are opened at the connection points and the substitution made. Y

A resistor R2 is connected to the control grid 24 of tube V2. The'other end of resistance R2 is bypassed to ground for radio frequency byl means of a condenser- 30 and it is also connected to one terminal of the secondary winding of transformer T. The other terminal of this secondary winding is connected through a source of negative bias 32 to ground. The'primary winding of transformer T is connected to a signal source A. The screen grid 34 of tube V2 is bypassed to ground for radio frequency by'condenser 38 and connected to a source of positive` potential not shownA which may be the same source connected to lead B. The anode 40 of modulator tube V2 is supplied with positive current and potential through resistance R3 and the coil L2 of tank circuit C2, L2 in Figs. 1, 3 and 4. In Fig. 2 the anode of V2 is tapped through a blocking condenser 44 on coil L2 and receives its positive current and potential supply through resistor R3.

In Fig. A1 the coil L2 is paralleled byvariable condensers C2, C3, C4 and C5 as shown. The connection between condensers C3 and C4 is grounded directly. The center point .of coil L2 is bypassed to ground through resistor R3 and a blocking condenser 46. The positive'current supl ply is connected to the circuit between resistor R3 and this blocking condenser 46. As stated before, the anode 40 of tube V2 is tapped on tube VI is connected to the crystal electrode at the lower partof coil L2. In Fig. 1 the other electrode of crystal X is connected (that is, coupled) to the modulator -tank circuit betwen condensers C2 and C3. This is the opposite end of the tank circuit from the end to which the anode 4l is connected. Likewise, the neutralizing condenser N is tapped on this tank circuit (on the same end of the tank circuit as the anode connection) between the condenser.; C4 and C5. The center connection point I4 between the crystal X and the neutralizing condenser N is, as stated, connected to the control grid GI of oscillator tube Vl.

In Fig. 3 and Fig. 4 the coil L2 is paralleled by lvariable condensers C3 andgCl and by fixed condensers Cl and C6.VV Thefcondensers C3 and C4 are preferably operated by one control shaft..

The connection between fixed condensers C and CI is grounded directly.

as for Fig. l. Likewise., the anode 4B oi' tube V2 is'connected to the lower end of coil L2 as shown. I'he other electrode of crystal X is connected or coupled to the tank circuit between condensers C2 and C5 (Figs. 3 and 4) while the neutralizing condenser N is connected to the tank circuit between conde'nsers C6 and C4. In practice, it is desirable to keep the middle condens-.ers C3, C4.

in Fig'. l and C5, C8 in Figs. 3y and 4 substantially identical. Likewise, the outer condensers C2, C5

infFig. 1 and C2. C4 in Figs. -3v and 4 should be alike.

denser C2. The centerof coil L2 may be connected to ground directly or through a blocking condenser I8.- 'Ihe crystal X and neutralizing condenser N are tapped oncoil L2 equal vdistances4v from the center or ground point. The crystal is tapped on the opposite side or the tank circuit i'rom that on which the anode 4l of-tube V2 is' coupled. e Y

In Figs. 1, 2,` 3 and 4 the operation of the crystal oscillator circuit with tube VI is the same. The operation of grounded anode crystal oscillator circuits has been described in prior art and need notbedescribed here. Y

The operation of the modulators in these cir-4 cuits requires either the use of a phase shiftingY network P in the grid excitation circuit of tube V2 or the slight detuning oi' the modulator tank circuit L2, C2, etc., to obtain the phase shift in the modulating radio-frequency excitation ener--l could be 90 degrees or any other angle in the leading direction depending on thetype of phase shifter P used). In passing through the tube V2 this energy is amplified and reversed substantially (180 degrees) in phase.Y After passing through the anode tank circuit L2, C2, C3, Cl, C5, the phase is again reversed substantially 180 degrees and then it is delivered to the crystal X with a lagging phase angle of about 90 degrees. Now the oscillating current from the grid of tube Vi passes through the crystal and through condenser C3 to ground. Since condenser C3 carries both the crystaloscillating current and the mod-- ulator tank oscillating current this is the element which couples the modulator tank circuit to the crystal oscillator circuit. The modulator current The coil L2 is by-passed to ground at its center point in the same manner In Fig. 2 the coil VL2 is paralleled by the conmodulator circuit L2, C2, etc., to the crystal oscilin condenser C3 and the crystal current in condenser C3 provide the two controlling voltage components. The excitation voltage on the control grid of oscillator tube VI is the resultant oi' these two components.

I In Figs. 2, 3 and 4 the phase shift is obtained by slightly detuning the modulator tank circuit L2, C2, etc., preferably on the low capacity side of resonance. In this case the phase of the excitation energy kon the control grid 24 oi modulator tube V2 is the same as that on the control grid GI of the oscillator tube Vi. In' passing through the modulator tube V2 this energy is ampliiled and reversed substantially (180 degrees) in phase.v If the modulator tank circuit was in tune it would produce a 180 degree phase reversal but since `the modulator tank circuit is slightly detuned it gives the excitation energy an additional phase rotation of say about degrees'in a direction depending on the direction of detuning. Consequently, the modulator and the oscillator components of the grid excitation are at approximately 90 degrees phase displacef is substantially equivalent to Fig. 1. In Fig. 3,

the phase of the excitation on the control grid 24 of modulatortube'VZ is the same as that on the control grid `Gi oi' oscillator tube VI. In passing Ythroughk modulator tube V2 this energy is amplined and" reversed substantially degrees in phase. Since the modulator tank circuit L2,C3, C4, C5, CS is slightly detuned it represents a reactance and the modulating excitation energy is given a further phase shift or rotation. It was found preferable to detune the modulator tank circuit on' the low capacity 'side of resonance so that it could be said to represent an inductive reactance.

Now, as stated before, the condenser C5 (Fig. 3) carries both modulator tank current and oscillator crystal and grid current, sothat thisy condenser acts asv coupling between the modulator and the oscillator circuits.j Also, the condenser C6 (Fig. 3), which carries theneutralizing condenserl current and the modulator tank current, and which is on the same end of the tank circuit 'as the anode connection; by like reasoning acts as the uncoupling between the modulator and the oscillator circuits.4 Neutralizing condenser N is adjusted to have substantially the same capacity as the crystal X. Since condensers C5 and C6 (Fig. A3) have the same capacity and also since the neutralizing condenser N and the crystal X have the same capacity the modulator circuit is` neutralized audit cannot aiect the crystal oscillator circuit unless the crystal is oscillating. YIn other words, the crystal must be oscillating before high frequency modulating excitationV energy can be transmitted from the lator' circuit. Therefore, this circuit insures crystal controlled frequency modulation.

Another advantage which this circuit has is that when modulator currents are cut oil the crystal oscillator will continue to function as long as it is supplied with steady electrode potentials. Now since the crystal oscillator circuit is coupled to the modulator circuit in the manner described above when the crystal is oscillating, the radiofrequency excitation potentials on the control grid of oscillator tube Vi is the resultant of the two excitation components, one from the modulator tank circuit and the other from the crystal oscillator circuit, the two components being disposed at say about 90 degrees phase angle?.l Since the modulator tank circuit is detuned in the direction stated above, it represents an inductive reactance and the modulating excitation energy in passing through it is rotated in phase say 90 degrees in the lagging direction. y Consequently, the phase of the modulator excitation component leads the oscillator excitation component by approximately 90 degrees.

As stated before, the radio-frequency excitation potential on the control grid of the oscillator tube VI is the resultant of these two excitation components. If the amplitudes of the currents and voltages in the modulator tube V2 are modulated by the signal oscillations from source A, the amplitude of the modulator excitation energy component delivered from the modulator circuit to the control vgrid of the oscillator tube Vi will also be modulated inamplitude according to the signal. There is another factor which has an effect on the phase angle of the modulator excitation energy component. The anode of modulator tube V2, being tapped across a portion of the inductance coil of the modulator tank circuit, constitutes a variable resistance across part of this inductance. Consequently,

during the process of modulation the variation of anode current in effect causes some change 361,506, led October 17, 1ilil, I have illustrated several modificationsV wherein the neutralizing condenser NC is omitted. These modifications l include also additional novel features not disclosed herein. For example, the piezo-electric crystal is elfectively in series with the grid and cathode of the tube V as illustrated in the sev-f eral modiilcations of the present application. In my said other application referred to above, the crystal is effectively shunted by the impedance between the grid GI and the cathode of tube Vi. I have found in working with a frequency modulator such as illustrated in Figs. 1.to 4, inclusive, and, in particular, inFigs. 3 and 4, that the neutralizing condenser C may also be used to adjust the amount of frequency swing or frequency modulation deviation. In other words, the amount of feedback from the modu- Y lator V2 and tank circuits L2, C2, etc., to they crystal X of the oscillator circuit, etc.,rmay be adjusted by means 'of changing the capacity of the neutralizing condenser N. This then affects the ability of the modulator to modulate the frequency of the crystal oscillator, Adjustment of the modulatoranode circuit is primarily lused to determine or produce the amount of frequency modulation deviation.

The neutralizing condenser N may comprise a capacity (variable condenser) or a crystal X, the capacity between the electrodes of which is adjustable and similar to the capacity between the electrodes of the crystal X. When a crystal is used for neutralizing purposes, the optical aids thereof is of such orientation that the crystal does .not oscillate.

tor relations, this causes the amplitude and the phase angle of the resultant grid excitation energy of the oscillator to vary according to the signal oscillations. lThese phase changes are added to each cycle of the oscillations and, consequently, cause a change in the frequency of the oscillations. For any value of modulator bias within the operating range, the frequency shift or change -is limited to a value where an equal and opposite excitation energy phase shift occurs which is caused by the opposite tuning of the various circuits due to the frequency change. There is also a limit to the possible total range of modulation caused by limitations in modulator tube current and by the angle of the excitation energy components. l

The output circuit CI, Ll of this frequency modulator is electronically coupled to the oscillation circuit by means of the anode I0 Aoi? tube Vi. This insures minimum reaction on the modushifting element is not included in the connection between the grid GI and grid 2l in Figs. l, 2, 3 and 4. When the phase shift is obtained by detlnlls the tank circuit, the excitation from resistor of about 20,000 ohms works best.

Moreover, I found during operation that a small air gap in the crystal holder gives a greater range of frequency modulation than a wide air In Fig. 4, I have illustrated a practical embodiment of a frequency modulator arranged in accordance with the present invention. The oscillation generation and frequency modulation portion of this circuit is similar to the modification illustrated in Fig. 3. Moreover, like parts have been designated by like reference characters in Figs. 3 and 4 and the operation of the oscillaton generator and frequency modulator illustrated in Fig. 4, it is believed, will be understood without further description. In Fig. 4, however, the output of the oscillation generator Vi comprising the tank circuit Ci, Li wherein the'frequency modulated wave energy appears is coupled by condenser to the grid electrode 63. of a radiofrequency amplifier tube 65. Negative bias potential is supplied to grid 63 through choke coil I2. In practice, I have found that a wire wound The anode 69 of thistube is connected as shown with a tank circuit comprising an inductive reactanc, 1l and a capacity reactance 12. The amplified frequency modulated wave energy is obtained from this tank circuit by means of coupling condenser 14 and output leads 16.

The audio-frequency signal source in Fig. 4 is connected to the modulator tube Vi by transformer T as in the prior modifications. However, in this modification, additional modulating means and circuit details are disclosed. The secondary winding of transformer T is connected to a switch III in such a manner that, in. one position, it is connected as shown with tone rectifier tube 8l to produce a rectified tone potential through low pass filter |02 across the resistors 86 and 88. These resistors are connected by leads 90 and 90' and switch contacts 9| and 9|' of switch W to the grid 2l o! tube V2 and to the grid oi' a compensator tube when tone keying is to be used. .Switch contact 9|' is connected to the grid of a compensator tube not shown. In the other position of the switch 80 the secondary winding of the transformer T isconnected directly across resistors |3-I3 and to leads 98 and 56' and from leads "and 96' by switch 8| to the grid 24 oi' tube V2 and by switch 9|' to the grid of the compensator tube not shown so that the oscillations generated may be modulated in accordance with voice signals. In other words, the triplepole double-throw switch 80 selects either voice modulation or tone signal modulation, whichever is desired. The double-pole multiple contact switch W permits modulation by voice signals, tone signals (spacing wave keying), relayed keyed spacing wave keying or steady dash for calibrating purposes.

Relay keying is accomplished by connecting the front and back contacts of the keying relay to the pair of leads and thereby to the control grid 2| of tube VI and through lead H to the grid of the compensator tube not shown. The compensator tube not shown in Fig. 4 is keyed in phase opposition to the modulator tube V2 so that a substantially constant current load is drawn from the anode power rectiiier. This permits a large amount of smoothing to be used without regard to voltage regulation requirements. Steady bias potentials are applied between the leads G and N for test and calibrating purposes and to supply xed bias potentials for spacing wave keying.

The low pass i'ilters |02 and I 03 are used in the tone and relay spacing wave keying circuits to eliminate or'reduce thehigher harmonic irequencies incidental to square wave keying in order 4to restrict the band of modulating frequencies.

The rrfnaining leads not discussed above in connection with Fig. 4 comprise means for supplying electrode potentials, etc.

The leads marked 115 v. at the left of Fig. 4 of the drawings serve as means for supplying alternating current to the thermostat control crystal temperature regulator at 80. The leads A and B are connected with the audio-frequency signal source used for modulation purposes. The

next lead designated by an E supplies negative bias potential when telephony modulation is carried out. The lead F supplies negative bias potential when tone signal keying isaccomplished. Leads G and N, as stated above, supply negative bias potentials for relay keying and for calibrating purposes. The lead H (connected by switch Si to lead H) is connected to the grid of a compensator tube such as for example shownin my United States application Serial No. 85,435, led June 10, 1936, now Patent No. 2,153,656, issued April, 1939. This compensator tube cooperates with the keying tube as disclosed in said application to regulate the drain on the source of direct current supplying the system when keyed.

Lead D supplies negative bias for the control grid of the amplier tube 65. Lead J supplies positive potential to the anode of tube Vi, while lead I supplies positive potential to the anode of the tube V2 and to the screen grids of all of the tubes. Lead K supplies positive potentials to the anode of tube 65 while leads L and M supply alternating current to the cathode heaters of all the tubes.

'I'he amplitude modulation incidentally caused by the frequency modulator is nearly al1 suppressed by tube 65 and that little which remains can be eliminated in a radio transmitter by the use of subsequent amplitude limiter stages such as the usual frequency multiplier stages. The frequency modulated carrier energy may then be ampliiied and/or multiplied in frequency in succeeding transmitter stages before it is delivered to the antenna.

Any suitable type of phase shifting network P may be used in these circuits. It may be of the type shown in Fig. 1 or like that shown in Fig. 5. It may instead be a series coil, parallel condenser arrangement. It may be a combination of resistances and coils or condensers or both. There may be only one stage or many stages in the phase sluiting network.

It should be noted that the terminating load on the phase shifting network P, such as the resistor R2 and the control grid capacity of the -modulatortube V2, affects the operation of the network and must be taken into consideration for phase shift calculations.

It may be noted in Figs. 3 and 4 that a condenser CO has been connected between the cathode of tube Vi and ground. This capacity seems to aid and strengthen the oscillator oscillations.

What is claimed is:

l. In a wave length modulation system, an oscillation generator of the electron discharge tube type having electrodes including a cathode and a control grid coupled in an oscillation generating circuit including a piezo-electric crystal and other electrodes coupled in an output circuit, an additional electron discharge tube having an anode and having a control electrode coupled to said generating circuit to derive excitation voltages therefrom, a circuit coupling the anode oi' said additional tube to said piezo-electric crystal to feed amplied excitation voltage to said crystal and from the crystal to the control grid of said rst tube, means for shifting the phase of the amplied voltage fed by said additional tube to said control grid, and means for controlling the gain Aoi said additional tube to modulate the wave length of the oscillations generated.

2. In a wave length modulation system, an oscillation generator of the electron discharge tube type having electrodes including a control grid coupled in an oscillation generating circuit including a piezo-electric crystal and having other electrodes coupled in an output circuit, a second electron discharge tube having an anode and having a control electrode coupled to said generating circuit to derive excitation voltages therefrom, phase shifting means in said last named coupling, a circuit coupled to the anode of said second named tube and to said piezo-electric crystal, .to feed excitation voltage by way of said crystal to said generating circuits, and means for controlling the gain of said second tube to thereby control the wave length of the oscillations generated.

3. In a wave length modulation system, an oscillation generator oi the electron discharge tube type having electrodes including a control grid coupled in an oscillation generating circuit including a piezo-electric crystal and having ther electrodes coupled in, an output circuit, a second electron;.. d ischarge tube.- having an anode and having, a control lelectrode coupled to said generating circuit to derive excitation voltages there- `from, a circuit tuned to a frequency slightly difierent from the mean frequency of operation of said. Oscillation generator coupled to the anode of said second namedtube and to said piezo-electric crystal to feed phase displaced amplied voltages tQsaid .crystal and to said generating circuit, ,and means to control the gain of said second tube inaccordance with signals to modulate the length .of the oscillations. generated.

4. In a wave. length modulation system, an

yoscillation generator of the electron discharge tube .type having electrodes including a control I grid coupled in an oscillation generating circuit including. a piezo-electric crystal and having other `.electrodes coupled in an output circuit electronically coupled to the generating circuit,

fasecondelectron discharge tube having an anode .andhavinga control electrode coupled to said generatingcircuit-to derive excitation voltages l cillation generator orthe electron discharge tube type'having electrodes coupled in an oscillation vgenerator .circuit including a piezo-electric crystal coupled betweentwo of the tube electrodes, and having other electrodes coupled in an output circuit, a second electron discharge tube having anjoutput electrode and having a control electrode coupled to'said-generating circuit to derive excitationl voltages therefrom, means coupling said output electrode of said second Vtube to an v electrode of said iirst tube by way of said crystal so that said crystal .and said second tube provide on said last mentioned electrode of said iirst tube two voltages the resultant oi which controlsv the frequency of operation of said generator, means for relatively shifting the phases of the said two voltages, and means ior modulating the impedance of the second tube to control the Wave length of the oscillations generated.-

6. In a wave generating and Wave length modulation system,v 4an electron discharge device havingelectrodes including an output electrode a cathode and a plurality of control electrodes, an oscillation circuit coupled between said cathode and pluralityof said control electrodes, one'of, which operates in said oscillation circuit as affariode, a piezo-electric crystal in said circuit, an' output circuit coupled with said output electrode, `a modulator tube having an anode, a cathode and a control electrode, a` circuit coupled to the anode and cathode of said modulator tube, means coupling a point on said last circuit to said piezo-electric crystal. an excitation circuit coupling said oscillation generating circuit to the control electrode of said modulator tube, and means for modulating the impedance of said second named tube in accordance with control potentials.

'7. In a wave generating and wave length modulation system, an electron discharge device having output electrodes including a cathode and having a plurality of control electrodes, an oscillation circuit coupled between said cathode-and a plurality of said control electrodes,one; of which operates in said oscillation circuit-as,A an anode, a piezo-electric crystal in said circuit,=an output circuit 'coupled .with said output electrodes and coupled to said oscillation circuit, by the electron stream of said tube, a modulator tube having an anode, a cathode and a control electrode, a tank circuit v `coupled to the anode and cathode of said modulator tube, meansecoupling a point on said tank-.circuit to said piezo-j electric crystal, an `excitation circuit gin'cluding -phase shifting means coupling .saidf oscillation circuit to a control electrode of said second vnamed tube, and means for modulatingthe impedance of said second named tube in accordance ,with control potentials. q n',

8. In a wave generating and wave length mod.-

ulation system, an electron discharge vdevicehaving output electrodes including a-cathodeand having va plurality of control electrodes, an 'scil.-

lation generating circuit coupled, between.: said cathode and a plurality of said controlelectrodes",4 one of which operates in said oscillation 'circuit'v asan anode, a piezo-electric crystal inV said .circuit, an output circuit connected `with saidoutgput electrodes and coupled to .said oscillationY generating circuit by the electron stream of said tube, a modulator tube having an anode, ..,a'

cathode and a control electrode, a tank circuit tuned to a frequency slightly diferentImmfthe frequency of operation of said generating circuit coupled to the anode and cathode of said modu- 'lator tube, a coupling betweenV said tank circuit and said piezo-electric crystal, an excitation circuit coupling said oscillation generating Acircuit to the control electrode of said second named tube, and means for modulating the impedance of 'said second named tube in accordance with control potentials. v v

9. In a wave generating and wave length modulation system, an electron discharge device having an anode, a cathode and a plurality ofgrid electrodes, an oscillation generating circuit coupled between la pairof said grid electrodesnd said cathode, a piezo-electric crystal included in said circuit, an output circuit coupled with said anode and cathode, a tank circuit comprising parallel inductance and capacity, means including said piezo-electric crystal kconnecting a point on said tank circuit to one of said grid electrodes of said oscillation generating. circuit, a neutralizing -condenser connecting said piezoelectric crystal to a second point on said tank circuit, a modulator tube having an anode, a cathode and a control grid,l means coupling said modulator tube anode to'a point on said tank circuit, means coupling the control grid of said l'modulator tube to a point on said oscillationv genlation circuit as an anode, a coupling between said one of said control electrodes and a point of substantially nxed radio-frequency potential, said cathode and other control electrodeoperating at` a radio-frequency potential above said nxed potential, an output circuit coupled with said anode and cathode and coupled to said oscillation circuit substantially by the electron stream only of said tube, a modulator tube having an anode, a cathode and control electrodes, a tank circuit tuned approximately to the frequency of operation of said oscillation circuit coupledto the anode and cathode of said modulator tube, a connection between a point on said tank circuit and a control electrode of said first named device, an excitation circuit connecting said oscillation circuit to a control electrode of said second named tube, and means for modulating the impedance of said second named tube in accordance with control potentials to modulate the frequency of the output oscillations.

11. In a wave generating and wave length modulation system an electron discharge device having a cathode anda plurality of control electrodes, an oscillation circuit comprising a piezoelectric crystal .iin a holder and an impedance in series between said cathode and one of said control electrodes, a connection of low radiofrequency impedance between another of said control electrodesl and ground radio-frequency potential, said other control electrode operating in said oscillation circuit as an anode, an output circuit-connected with said anode and cathode ofsaid tube, a modulator tube having an anode-a cathode and a control electrode, a tank circuit tuned substantially to the frequency of said operation of oscillation circuit coupled to the anode and cathode of said modulator tube, a connection between one terminal of said pieno-electric crystal and a point on said tank circuit spaced from the point thereon to which said anode of said modulator tube is coupled, a neutralizing condenser coupling the other terminal of said crystal to a point on said tank circuit, an excitation circuit coupling said oscillation circuit to the control electrode of said second named tube, and means for modulating the impedance of said second named tube in accordance with control potentials.

12. In a wave length modulation system, an oscillation generator of the electron discharge tube type having electrodes including a control grid coupled in an oscillation generator circuit including a piezo-electric crystal between said control grid and another electrode, an additional electron discharge tube lhaving an anode andhaving a control electrode coupled to said aforesaid circuit to derive excitation voltages therefrom, a cou-A I.

pling including said crystal in series between the anode of said additional tube and the grid of said nrst tube to feed voltage from said additional tube to said generator, means for shifting the.

phase of the excitation voltage fed by said additional tube to-` said generator, and means for modulating the impedance of the additional tube Ain accordance with signals.

13. In a wave generating and wave length modulation system, an"l oscillation -generator comprising, an electron,l,discharge device having a cathode. an output electrode, and a control electrode, an oscillation circuit coupled with electrodes of said 'device including said cathode and said control electrode, a piezo-electric 'crystal in said circuit, an output `circuit cgiipled with said output electrode and cathode, a modulator tube having an anode, a cathode and a control electrode, means for limpressing voltages of the genimpressing voltages relayed by said modulator tube on said crystal, means for introducing a phase displacement of` about degrees in the voltage impressed on said crystal, and means for modulating the potential on an electrode in said tube in accordance with signals.

14. In a wave generating and wave length modulation system, an oscillation generator comprising, an electron discharge device having a cathode, an output electrode, and a control electrode, an oscillation circuit `coupled with electrodes of said device including said cathode and said control electrode. a piezo-electric crystal and an impedance in said circuit, an output circuit coupled with said 'output electrode and cathode, a modulator tube having an anode, a cathode and a control electrode, a coupling between said control electrode of said modulator tube and one of said circuits, an output circuit including said impedance coupled to the anode of said modulator tube, said impedance in said oscillation circuit and modulator tube outputr circuit serving to couple said circuits to feed amplified voltage from said modulator tube to said generator, phase displacing means in one ot said last two couplings, and means for modulating the potential on an electrode in said tube in accordance with Signals.

15. In a wave generating and wave length modulation system, an oscillation generator comprising, an electron discharge device having a cathode, an output electrode, and a control electrode, an oscillation circuit coupled with electrodes of said device including said cathode and said control electrode, a piezo-electric crystal in said circuit in series between said controlgrid and cathode, an output circuit coupled with said output electrode and cathode, a modulator tube having an anode, a cathode and a control electrode, s. coupling including an impedance between said control electrode of said modulator tube and one terminal of said crystal, s. phase' shifter insaid coupling, an inductance, a coupling between the anode of said modulator tube and a point on said inductance, a coupling between a point on said inductance and the other terminal of said crystal, and means for modulating the potential on an electrode in said tube in accordance with signals.

16. In a wave length modulation system, an oscillation generator of the electron discharge tube type having electrodes including a control grid coupled in an oscillation generating circuit including a piezo-electric crystal and having other electrodes coupled in an output circuit, an additional electron discharge tube having an anode and having a control electrode coupled to said generating circuit to derive excitation voltages therefrom, a circuit tuned to a frequency slightly diil'erent from the mean frequency of operation of said oscillation generator, a coupling between a point on said tuned circuit and the anode of said second named tube, a coupling between a different point on said tuned circuit and said oscillation generating circuit. a connection between a point on said tuned circuit and the cathodes of both oLsaid tubes, and means to controlthe gain-of said-additional tube in accordance with signals to thereby modulate the length of the oscillations generated.

17; In a wave length modulation system, an electron discharge device having oscillation generating electrodes, an oscillation generating circuit, including a frequency controlling piezo-electric crystal, regeneratively coupled to 'said electrodes, the generated voltage phase on at least one of said electrodes being of a certain phase, means for deriving voltage of the generated frequency from said circuit and feeding said derived voltage by way of said crystal backA to said vone of said electrodes whereat the generated volte prising a piezo-electric crystal, a reactance, and' an impedance in' series betweensaid cathode and said control electrode, and a circuit. including said impedance between saidv cathode andl said electrode serving as an anode, an output circuit Acoupled with said oscillation circuit, and means for modulating the length of the oscillations generated including, a modulator tube having an anode, a cathode and a controlelectrode, a tank circuit, comprising a reactance Asliunted by said iirst reactance, coupled to the anode and cathode of said modulator tube, said rst reactance providing a coupling between the said tank circuit and the oscillation circuit, an excitation circuit coupling said oscillation circuit to said control electrode of said modulator tube, and means for modulating the impedance of said modulator tubein accordance with control potentials.

19. In a wave generating and wave length mcdulation system, oscillation generating means including an electron discharge device having a cathode, an electrode serving as an anode,y and a control electrode, an oscillation circuit comprising a piezo-electric crystal, a reactance, and an impedance in series between said cathode and said control electrode, and a circuit including said impedance between said cathode and said electrode serving as an anode, a reactance in shunt to said impedance for improving the operation of said generating means, an output circuit coupled to said oscillation circuit, a modulator tube having an anodeLa cathode and a control electrode, a tank circuit, comprising a reactance shunted by said rst reactance, coupled to the anode and cathode of said modulator tube, said first reactance providing a coupling between said tank circuit and the oscillation circuit, an excitation circuit coupling said oscillation circuit to said control electrode of said modulator tube, and means for modulating the impedance of said modulator tube in accordance with control potentlals.

20. In a wave generating and wave length modulation system, oscillation generating means including an electron discharge device having a cathode, an electrode serving as an anode, and a control electrode, an oscillation circuit comprising,a piezo-electric crystal, a reactance, and an impedance in series between said cathode and said control electrode, and a circuit including said impedance between said cathode and said electrode serving as an anode, an output circuit coupled with said oscillation circuit, and means for modulating the length ofA the oscillations generated including a modulator tube having an anode, a cathode and a control electrode, a tank circuit, comprisinga reactance shunted by said first reactance, coupled to the anode and cathode of said modulator tube, said irst reactance providing a coupling between the said tank circuit andthe oscillation circuit, an excitation circuit coupling said oscillation-circuit to said control electrode of said modulator tube, a multiple stage phase shifter in said excitation circuit coupling and means for modulating the impedance ofsaid modulator tube in accordance withv control potentials.

21. In a wave generating and Wave length modulation system, oscillation generating means including an electron discharge device having a.

cathode, an electrode serving as an anode, and a control electrode, an oscillation circuit includlng a piezo-electric crystal regeneratively coupling saidV control electrodeesaid electrode serving as an anode and said cathode for the production of sustained` oscillations, an output circuit coupled to said oscillation circuit, and

means for modulating the length of the oscil- V lations generatedin accordance with signals inf cluding, a. source of signals, a modulator tube having ananode, a cathode and a control electro-de, an'excitation circuit coupling said oscillation circuit to said control electrodey oi' said modulator tube to feed toy said control electrode voltages of the generated frequency, a coupling between the cathode of said device and said tube.

a high frequency circuit including said crystal` coupling the anode of said tube to the control electrodey oi' said device and connections coupling said source of signals to said modulator tube to modulate the conductivity thereof in accordance with' signals.

22. In a wave generating and wave length modulation system, an electron discharge device having a cathode, an anode, and a plurality o! control electrodes, an oscillation circuit comprising, a piezo-electric crystal, an inductance and an impedance in series between said cathode and one of said controlelectrodes and a connection including said impedance between the other of said control electrodes and said cathode, an output c'ircuit connected with said anode, a modu- I having a cathode, an anode, and a plurality of to said oscillation generation circuit by the electron stream of said tube, a modulator tube havcontrol electrodes, an oscillation lcircuit comprising a piezo-electric crystal, a reactance, and an impedance in series between said cathode and one of said control electrodes, and a circuit including said impedance between said cathode and the other of said control electrodes, an output circuit connected with said anodel and coupled ing an anode, a cathode and a control electrode, a tank circuit, comprising a second reactance shunted by said first reactance, coupled to the anode and cathode of said modulator tube, an excitation circuit coupling said oscillation circuit to said control electrode of said modulator tube, and means for modulating the impedance of said `odulator tube in accordancewith conf 24. In awave. generating and Wave length modulation system, an electron discharge device lhaving an anode, a cathode and-a plurality; vof grid electrodes. an oscillation 'generating cir- 'v cuitcomprisingV a piezo-electric crystal and 4a v.reactance in series between one'of said grids -,and said' cathodefand anirnpedance between .an-

other .of said 1grids and said cathode, an'out` put circuit connected with said anode and cathode, ,a tank circuit comprising a secondjreact- `ance 'shuntedby said flrst reactance, a moduilato;tubewhaving an anode, a cathode and Ya. conftrol' grid,- means 'connecting said modulator tube anodev kto apoint on -said tank circuit, means ouplingtheicontrol 'grid 'of said modulator tube toa point= on said impedance, 4and means for modulating thev impedance of .said modulator tube inv-,accordance with' control potentials to thereby modulate vthelength of. the waves generated. v' l 25.` In a wavegenerating and wavev length modulation system, an electron discharge device having a cathode, an -anode and two auxiliary tially by electron stream only of said. tube,

`a` modulator tube having an anode, a cathode andra control electrode, a tank circuit including said reactance tuned approximately to the frequency of; operation-of oscillation of said oscillation.i rcuit,.means coupling-the anode of said second'tubeto a pointon said tank circuit, an

excitation circuit connecting said oscillation eirtrode operating `above said fixed potential, an output circuit con- -.tosaid oscillation generation circuits substancuit toa control electrode of said second named tube, and meansfor modulating the impedance of said-second'named tube in accordance with control potentials to modulate the frequency of the output oscillations, f

26; In, a Wave generating and' Wave length Imodulation system. an electron discharge device havinga cathode, ananode and two auxiliary electrodes, an oscillation circuit including a piezo-electric crystal and a capacity in series between said auxiliary electrodes, a connection between aipointv on. said circuit and the cathode of Asaid device, the tuning of said oscillation cir- ,cuit being determined primarily by said crystal, oneof saidA auxiliary electrodes operating in said oscillation circuit as an anode, a connection between said one of said auxiliary electrodes and a point o f substantially fixed radio-frequency potentiahs'aidcathode and other auxiliary elec a radio-frequency potential nected withsaid anode and cathode and coupled to said oscillation circuit substantially by the electron stream only of said tube, a modulator tube having an anode, a cathode and a control electrodaa tank circuit comprising an inductance and a 'capacity in series with said first namedcapacity in shunt to said inductance, means coupling the anode of said'second tube to a point on the inductance of said tank circuit, anexcitation circuit connecting said oscillation generating circuit to the control electrode of said modulator tube, and means for modulating the potential ofthe control electrode of said modulator tube inaccordance with control potentials tdmodulate the frequency of the oscillations vin vsaid output circuit.

GEORGE L. UssLMAN. 

